The purpose of this project is to study the mechanisms and the limitations of a variety of physical activities in old and young individuals. Muscular activity ranges from brisk walking on an inclined treadmill to tapping between targets of various widths drawn on paper and separated by various distances. Exercise responses are measured for blood pressure, heart rate, pulmonary ventilation, carbon dioxide elimination, and oxygen uptake. The oxygen cost of exercise is measured and compared to the total amount of physical work performed to estimate the mechanical efficiency of the subjects' neuromuscular and psychomotor control systems. Responses of the pulmonary system are interpreted in terms of standard spirometry and dead space (residual volume) measurements as well as studies of respiratory control. Limitations on performance imposed by cerebrovascular, cardiovascular, and pulmonary disease are assessed. Reflex time, reaction time and speed and accuracy of movement are measured and compared with exercise responses.